The present invention relates to a silicone emulsion composition for surface release treatment or, more particularly, to a silicone emulsion composition suitable for surface release treatment of various kinds of substrates having excellent stability relative to the pot life and shelf life along with good curability of the surface film formed therefrom even after intense mechanical working.
It is a well established technology that the surface of various substrates such as sheets of paper, plastics and the like coming into contact with a sticky substance is coated with a surface-release silicone composition with an object to prevent adhesive sticking therebetween. The surface-release silicone compositions currently under practical applications are mostly of the solution type by using a large volume of an organic solvent. A serious problem in the use of these surface-release silicone compositions is that the organic solvent not only causes pollution of the atmospheric air but also is undesirable in respect of the safety in the working environment and workers' health due to the inflammability and toxicity of the organic solvent because recovery of once vaporized solvents is almost impossible unless very expensive facilities are installed even by setting aside the problem of the expensiveness of organic solvents in general.
With an object to avoid the above mentioned problems due to the use of an organic solvent, silicone emulsion compositions for surface-release treatment without using any organic solvents have been proposed including those of the condensation reaction-curable type and the addition reaction-curable type. The silicone emulsion compositions of the condensation reaction-curable type are defective in the relatively short pot life so that they can be used in limited applications. On the other hand, those of the addition reaction-curable type are advantageous in respect of the relatively long pot life so that several different methods have been proposed for the preparation thereof. For example, Japanese Patent Publication 57-53143 proposes a method in which a mixture is prepared from a first aqueous emulsion comprising water, a vinyl-containing organopolysiloxane, a platinum compound as a catalyst and an emulsifying agent and a second aqueous emulsion comprising water, an organohydrogenpolysiloxane, a platinum compound as a catalyst and an emulsifying agent. Japanese Patent Kokai 54-52160 discloses a surface-release silicone emulsion composition prepared by the method of emulsion polymerization. Further, Japanese Patent Kokai 63-314275 teaches a method in which a vinyl-containing organopolysiloxane and an organohydrogenpolysiloxane are jointly emulsified in water by using a specific emulsifying agent and this emulsion is then admixed with an aqueous emulsion of a platinum compound as the catalyst.
The silicone emulsion composition prepared by the first of the above mentioned methods is not always quite satisfactory because the pot life and shelf life of the composition cannot be long enough as desired along with a rather poor curability. A problem in the last of the above mentioned methods is that an emulsifying agent having high purity is required and only limited emulsifying agents can be used therefor.